THE INFLORESCENCE, AND THE FLOWER 231 



(ii) Meristic differences. The number of parts in each successive 

 category may differ in different flowers, and these are called meristic 

 differences. In spiral types the numbers are relatively large and 

 indefinite (Fig. 180) ; in cyclic types they are smaller, and usually 

 definite (Fig. 178). Where the whorls are well defined the actual 

 numbers of parts in each may be compared, and are found to vary 

 in different flowers. Some fundamental number, commonly three, four, 

 or five, then rules in the construction of each flower. Such flowers 

 may be described as trimerous, tetramerous, or pentamerous re- 

 spectively. But the fundamental number rarely holds through all the 

 whorls, though the Flax is an example of this (S 5 , P 5 , A 5 , G 5 ). 

 Usually the androecium shows larger, and the gynoecium smaller 

 numbers than the sepals or petals. 



Not only are meristic differences common between different families, 

 genera, or species, but even between different flowers of the same inflorescence. 

 As regards families, the Crassulaceae show meristic variation in high degree, 

 the fundamental figure rising in the House-leek to as many as twenty, whereas 

 in Sedum it is commonly five. Within the family of the Liliaceae Maianthemum 

 has 2-merous flowers, most Liliaceae have 3-merous, but Paris has 4-merous, 

 or even 5-merous flowers. Within the Primulaceae Glaux sometimes has 

 4-merous, Primula 5-merous, and Lysimachia 6-merous flowers, and others 

 have still higher numbers. Within the genus, Gentiana campestris has 

 4-merous, and G. amarella 5-merous flowers, while species of Saxifraga may 

 show flowers 5-, 6-, or y-merous. In the same inflorescence Adoxa and Ruta 

 both show meristic variation. In Ruta the terminal flower is 5-merous, and 

 the lateral flowers 4-merous. In Adoxa, as a rule, the terminal flower is 

 4-merous, and the lateral flowers 5-merous. Such facts are a warning 

 against any undue faith in numbers of parts as themselves indicative of 

 affinity. 



(iii) Fusion of Parts. In some simple flowers like the Buttercup 

 all the floral parts are separate, or free from one another. This state 

 is probably primitive, and corresponds to the condition seen in most 

 vegetative buds. But in many flowers certain parts are found to be 

 fiised together in the mature state. There is a real continuity of 

 tissue between them. A familiar instance is the Primrose, where the 

 corolla can be pulled away in one piece, though its margin clearly 

 shows five petaline lobes. Further, if the corolla of the Primrose be 

 opened out, five stamens will be seen attached to the inner surface of 

 its tube. So not only is there a cohesion of the five petals to form a 

 tubular corolla, but also an adhesion of the stamens to it. COHESION 

 of parts of the same category (such as petals with petals], and ADHESION 

 of parts of different category (such as stamens to petals] , are common in 



